Azerbaijan says Armenian forces have used white phosphorus weapons in the fighting over the Nagorno-Karabakh region and is calling for an international investigation.

Fighting escalated sharply last month, killing at least 75 soldiers. It was the worst outbreak of hostilities since a 1994 cease-fire ended a full-scale separatist war.

Nagorno-Karabakh is in Azerbaijan, but since 1994 has been under the control of local ethnic Armenian forces and the Armenian military.

Foreign Ministry spokesman Hikmet Hajiyev told journalists on Wednesday that Azerbaijan had found a white phosphorus round in a field and it is asking the Organization for Security and Cooperation in Europe to investigate.

White phosphorus artillery can be used as illumination rounds, troop cover or for incendiary purposes. The rounds can cause severe burns and gas poisoning.